Bats

Bats are a critical element in nature’s delicate web of life. The only major predator of night-flying insects, bats often consume over half their body weight in insects each night, and are important for controlling insects that affect crops, forests and humans.

Northern Virginia area bats are in decline, due primarily to loss of habitat and disturbance by humans. However, Little Brown Bats and Tricolored Bats have suffered substantial additional losses from white-nose syndrome (WNS), and have declined by more than 95% since 2009. WNS is a fungal disease that affects hibernating cave bats.

Bats are nocturnal, and the best time to see them is just after sunset as they leave their roosts to feed. They catch their prey in flight and often feed over fields, open water and around street lights, where insects swarm. Some species also forage in the tree canopy or in corridors through forest. A typical bat may consume over 500 insects in just one hour, nearly 3,000 in a single night.

Bats and Their Life Cycles

Bats are the only mammals able to fly. Compared to other small mammals that produce many young each year but live only 1-2 years, bats typically have a single litter of one or two young per year, and can live in the wild for over 20 years. Their low reproductive rates make it difficult for populations to recover quickly after large declines.

In spring, bats migrate back to Loudoun County from places south, or emerge from hibernation in trees and caves. During their time here, bats live in and around forests, wetlands, fields and buildings.

Pregnant females, who mated the previous fall, seek sheltered roosts in buildings, tree cavities and tree foliage to raise their pups. In some species, females gather in maternal colonies, which can be small to thousands. Males remain solitary throughout the season.

Because insects are few during the winter, area bats either migrate or hibernate. For Little Brown Bats, Big Brown Bats and Northern Myotis, maternity colonies disband in late summer and early fall and the bats travel to the hibernation places. This is the time when males and females join, sometimes in very large groups. For our bats that migrate, the Silver-Haired, Eastern Red, and Hoary bats begin their migration to warmer climates.

Echolocation

Bats can see quite well but rely on their hearing at night. Echolocation enables them to use their well-developed ears to navigate and catch moving prey in darkness. A bat’s echolocation system uses ultrasonic sound pulses and echoes to maneuver and catch insects while avoiding flying into objects.

Bats & Human Contact

Left alone, bats are harmless and avoid contact with humans. Occasionally, single bats enter a house; a maternity colony roosts in a building; or a bat may be found on the ground. All these situations can be safely resolved without killing the bats. Information on the proper techniques for handling these situations can be found at here and here.

Bats in Loudoun County

Bats are a diverse group with over 1,000 species worldwide; 15 species are native to Virginia, and 7 species are known to reside in Loudoun County, including:

Little Brown Bat (Myotis lucifugus) is small, about 3½” long, with glossy, brown fur. They often roost in buildings, tree cavities and crevices, tunnels, abandoned mines, and cliffs, and are the species most likely to be found near homes and in bat houses. They forage at late dusk, over trees, lawns, pastures and open water. Just one bat can eat up to 1,200 insects in an hour, including moths, mosquitoes, flies, beetles and aquatic insects. In October/November, they gather in caves, tunnels and mines to hibernate. Once the most common bat in North America, they have been severely decimate by White Nose Syndrome.

Big Brown Bat (Eptesicus fuscus) is a larger bat, 4-5” long, with long, glossy, dark-brown hair, a broad nose, and short black ears. Traditionally, Big Brown Bats formed nursery colonies beneath loose bark and in small tree cavities, but have also adapted to manmade structures as forests have disappeared. Today, nursery colonies can be found in barns, houses, caves and abandoned mines. Big Brown Bats don’t migrate and may use the same roost for summer and winter. They fly at dusk, feeding over water, land and forest, and begin hibernating in late October.

Eastern Red Bat (Lasiurus borealis) is a medium-sized bat, 3½-4¾” long, with bright red to rusty long, silky fur. The tree-dwelling bats live mostly in dense foliage and hibernate in the open or under leaf litter. They can be hard to spot when clinging to trees, looking like a fall leaf or pine cone. Red Bats are solitary except for mating and migrating. They fly in early evening, feeding in the forest, around lights near buildings, and on the sides of barns; eating hard and soft insects, with moths being a favorite. They migrate south in late September to November.

Bats less common in Loudoun County include:

Silver-Haired Bat (Lasionycteris noctivagans) is medium-sized, 3¾-4½” long with long, brownish-black, silver-tipped fur. The tree bats depend on old-growth forest, and managing forests for diverse age, allowing snags to remain, and maintaining forested corridors is critical to them. They are rarely seen around homes. Females form small nursery colonies in tree cavities. Silver-Haired Bats fly slowly near mixed or coniferous forests adjacent to water, and are frequently found around streams, rivers and woodland ponds. They feed earlier than most bats, mostly on beetles, and often emerge just before sunset. They migrate south for the fall and winter.

Northern Myotis (Myotis septentrionalis) is a medium-sized bat, 3-5” long, with light brown fur. They need dense forest stands for their habitat, and forage on hillsides and ridge-forests. Females form small colonies under bark and in tree cavities. They hibernate singly, in small clusters, or in colonies of up to 350 individuals, as early as August, in caves and mines.

Hoary Bat (Lasiurus cinereus) is the largest of our Loudoun bats, 5-5½” long. The fur is long and dark to light brown, with gray or silver tips, which gives a frosted (“hoary”) appearance. Hoary Bats feed above trees, over water and in forest clearings, emerging after dark. They feed on moths, mosquitoes, dragonflies, wasps, beetles and grasshoppers. Hoary Bats are strong, swift fliers that migrate south for the winter. They are encountered in Virginia usually during migration, as most seem to go farther north to give birth.

Tricolored Bat (Perimyotis subflavus) is our smallest bat, 2¾-3¾” long, with yellowish-brown tricolor fur. They usually roost in caves, rock crevices and tree foliage, and forage in early evening in treetops. Tricolored Bats are active until late October, and hibernate in caves often too tiny for other species.

Ways to Help

Help protect hibernation and foraging habitat including open fields, large contiguous forest areas, roost trees, farms, streams and ponds

Let dead trees stand. If there is no danger to persons or buildings, leaving dead trees, called snags, standing provides habitat for bats, cavity-nesting birds, small mammals, and bark-dwelling insects.

Avoid the use of pesticides that kill bats’ forage and can poison bats

Read books about bats and attend educational programs to learn more.

Install a bat house. Plans for building multi-chamber houses, which work well with our local species, can be found on the website of Bat Conservation International; their booklet “The Bat House Builder’s Handbook” by Merlin Tuttle, is another good resource. Bat houses sold in stores typically do not work because they are single chamber or too small. The website of Bat Conservation and Management shows why most commercial boxes don’t work, and sells kits that, according to Loudoun Wildlife Conservancy, are very good.

(compiled from sources including Loudoun Wildlife Conservancy’s “Bats of Loudoun” and “A Homeowners Guide to Northeastern Bats and Bat Problems,” Penn State College of Agricultural Sciences)